PALEOBOTANICAL EVIDENCE 5 L9 



are referred to the Scliiz^acete, now almost wholly tropical. GleicJi- 

 enites of the Gleicheniaceae is mainly tropical. Laccopteris and Matoni- 

 dium of the Matoniace^ have the living representatives wholly tropical. 

 Coniopteris and Dicksonia of the Cyatheacese are mainly tropical and 

 subtropical. Dictyophyllum and Hausmannia of the family Dipteraceai 

 have the living forms wholly tropical. 



Besides these there are other genera not so definitely placed, such as 

 Polypodium, Scleropteris, Adiantites, Tseniopteris, Sagenopteris, Danaeop- 

 sis, etcetera. These have been characterized on the basis of resemblance 

 to the living forms (Polypodium, Adiantum, Taenia, Danaea, etcetera), 

 and on this basis there is no reason to suppose they lived under condi- 

 tions greatly unlike the habitat of the living analogues. 



The Jurassic cycads are abundant in types as well as individuals, 

 whence, of course, the designation of the Jurassic as the age of cycads. 

 Approximately 25 genera of cycads are known from the Jurassic, includ- 

 ing trunks so preserved as to exliibit all details of internal structure' 

 and reproduction, separate flowers (Williamsonia), and leaves, cones, 

 and seeds of many types. The living cycads number 10 genera and 

 about 80 species, and are essentially tropical in their present .distribu- 

 tion, though a few forms are able to endure moderate cold or even frost. 



The Ginkgoales is represented by a single genus (Ginkgo) and a single 

 living species now confined to Japan, though there is some doubt as 

 to its occurring in a wild state. It has, however, been grown for orna- 

 ment in many mainly warm temperate parts of the world, although it 

 can withstand several degTees of frost. Ginkgo is very abundant in the 

 northern Jurassic and shows great diversity of leaf -forms, many of which 

 have been given specific standing, though it is perhaps doubtful whether 

 they should not be considered as representing a single polymorphous 

 species. 



The Coniferae, although numbering twenty or more nominal genera, 

 were not an especially dominant element in this flora, and a number of 

 them are so fragmentary and badly preserved that their affinities can not 

 be made out with satisfaction. All things considered, however, they 

 appear to belong mainly to types that now find a congenial habitat in 

 warm, not to say subtropical, lands. 



Based on the above facts the following conclusion is reached regarding 

 the probable climatic conditions during Jurassic time: The presence 

 of luxuriant ferns, many of them tree-ferns, equisetums of large size, 

 cycads, and conifers, the descendants of which are now found in southern 

 lands, all point to a moist, warm, probably subtropical climate. 

 XXXVI — BuTX. Geol. Soc. Am., Vol. 30, 1918 



